The blood glucose concentration is an important marker for diabetes. In the determination of a blood glucose concentration, a glucose oxidase has conventionally been used. However, such a glucose oxidase is affected by a dissolved oxygen concentration and an error is caused in the measured value. Therefore, a glucose dehydrogenase which is not affected by oxygen has also been widely used recently.
As a commercially available glucose dehydrogenase which is not affected by oxygen, a glucose dehydrogenase which requires pyrroloquinoline quinone (PQQ) as a coenzyme (PQQ-GDH) is known, however, a conventional PQQ-GDH has a disadvantage that it reacts also with sugars other than glucose such as maltose and galactose.
As a countermeasure against this disadvantage, the group of the present inventors found a novel soluble GLD which requires FAD as a coenzyme from Aspergillus terreus FERM BP-08578 strain (Patent document 1) and succeeded in cloning of a gene (Patent document 2). Such a GLD has unprecedented excellent properties that it is not affected by dissolved oxygen, oxidizes a hydroxy group at the 1-position of glucose, and has a low activity (enzymatic activity) for maltose and galactose.
Further, it is shown that the glucose dehydrogenases derived from Penicillium lilacinoechinulatum NBRC 6231, Penicillium italicum NBRC 32032, and Aspergillus oryzae TI strains disclosed in Patent document 3 and the glucose dehydrogenase derived from Aspergillus oryzae BB-56 strain disclosed in patent document 4 also have a low activity for maltose and galactose.
However, there was still a problem that the substrate specificity of these conventional GLDs should be improved.
Patent document 1: WO 2004/058958
Patent document 2: WO 2006/101239
Patent document 3: WO 2007/116710
Patent document 4: WO 2007/139013